Class KeyGenerator

This class provides the functionality of a secret (symmetric) key generator.

Key generators are constructed using one of the getInstance
class methods of this class.

KeyGenerator objects are reusable, i.e., after a key has been
generated, the same KeyGenerator object can be re-used to generate further
keys.

There are two ways to generate a key: in an algorithm-independent
manner, and in an algorithm-specific manner.
The only difference between the two is the initialization of the object:

Algorithm-Independent Initialization

All key generators share the concepts of a keysize and a
source of randomness.
There is an
init
method in this KeyGenerator class that takes these two universally
shared types of arguments. There is also one that takes just a
keysize argument, and uses the SecureRandom implementation
of the highest-priority installed provider as the source of randomness
(or a system-provided source of randomness if none of the installed
providers supply a SecureRandom implementation), and one that takes just a
source of randomness.

Since no other parameters are specified when you call the above
algorithm-independent init methods, it is up to the
provider what to do about the algorithm-specific parameters (if any) to be
associated with each of the keys.

Algorithm-Specific Initialization

For situations where a set of algorithm-specific parameters already
exists, there are two
init
methods that have an AlgorithmParameterSpec
argument. One also has a SecureRandom argument, while the
other uses the SecureRandom implementation
of the highest-priority installed provider as the source of randomness
(or a system-provided source of randomness if none of the installed
providers supply a SecureRandom implementation).

In case the client does not explicitly initialize the KeyGenerator
(via a call to an init method), each provider must
supply (and document) a default initialization.

Every implementation of the Java platform is required to support the
following standard KeyGenerator algorithms with the keysizes in
parentheses:

AES (128)

DES (56)

DESede (168)

HmacSHA1

HmacSHA256

These algorithms are described in the
KeyGenerator section of the
Java Cryptography Architecture Standard Algorithm Name Documentation.
Consult the release documentation for your implementation to see if any
other algorithms are supported.

getInstance

Returns a KeyGenerator object that generates secret keys
for the specified algorithm.

This method traverses the list of registered security Providers,
starting with the most preferred Provider.
A new KeyGenerator object encapsulating the
KeyGeneratorSpi implementation from the first
Provider that supports the specified algorithm is returned.

getInstance

Returns a KeyGenerator object that generates secret keys
for the specified algorithm.

A new KeyGenerator object encapsulating the
KeyGeneratorSpi implementation from the specified Provider
object is returned. Note that the specified Provider object
does not have to be registered in the provider list.

init

If this key generator requires any random bytes, it will get them
using the
SecureRandom
implementation of the highest-priority installed
provider as the source of randomness.
(If none of the installed providers supply an implementation of
SecureRandom, a system-provided source of randomness will be used.)

init

public final void init(int keysize)

Initializes this key generator for a certain keysize.

If this key generator requires any random bytes, it will get them
using the
SecureRandom
implementation of the highest-priority installed
provider as the source of randomness.
(If none of the installed providers supply an implementation of
SecureRandom, a system-provided source of randomness will be used.)

Parameters:

keysize - the keysize. This is an algorithm-specific metric,
specified in number of bits.